PASADENA, Calif., Nov. 5 (UPI) -- NASA officials said all the scientific tools on the two Mars Exploration Rovers are still working well, a full 10 months after they landed on the planet.
The instruments on Spirit are continuing to add fresh evidence about the history of the layered bedrock on a hill the rover currently is climbing.
"Our leading hypothesis is that these rocks originated as volcanic ash that fell from the air or moved in ground-hugging ash flows, and that minerals in them were altered by water," said Ray Arvidson of Washington University in St. Louis, deputy principal investigator for the mission.
"This is still a working hypothesis, not a firm conclusion, but all the instruments have contributed clues that fit," he said.
Both Spirit and its twin rover, Opportunity, completed their three-month primary missions in April. NASA has extended their missions twice because they have remained productive longer than anticipated.